Kirkegaardia franciscana, Blake, James A., 2016

Blake, James A., 2016, Kirkegaardia (Polychaeta, Cirratulidae), new name for Monticellina Laubier, preoccupied in the Rhabdocoela, together with new records and descriptions of eight previously known and sixteen new species from the Atlantic, Pacific, and Southern Oceans, Zootaxa 4166 (1), pp. 1-93 : 44-47

Kirkegaardia franciscana new species

Figures 21–22

Monticellina sp. 2: Hilbig & Blake 2006: 262; Blake et al. 2009: 1796.

Material examined. California continental slope west of the Farallon Islands, San Francisco Deep Ocean Disposal Site (SF-DODS) 2003 monitoring survey, R/ V Point Sur, Sta. 19, 37º37.97′N, 123º30.04′W , 2983 m, 24 September 2003, coll. J.A. Blake, holotype and 3 paratypes (LACM-AHF Poly 8921–2); 2004 monitoring survey, R/V Point Sur, Sta. 52, 37º44.00′N, 123º28.00′W, 2237 m, 0 3 October 2004, coll. J.A. Blake, 3 paratypes (LACM- AHF Poly 8923).

Description. A small, elongate, threadlike species ( Figs. 21 A–B, 22A); holotype complete, 1.5 mm long, 0.11 mm wide for 26 setigerous segments; most paratypes complete, similar in size and number of segments. Color in alcohol opaque white; no pigment present.

Pre-setigerous region about 1.5x as long as wide; prostomium a conical lobe, narrowing to rounded tip ( Figs. 21 A, 22A–D); eyes absent; nuchal organs observed in two paratypes as darkly pigmented areas at posterolateral margins ( Fig. 22 C). Peristomium expanded, relatively smooth, with one partial lateral groove, but no distinct annulations ( Fig. 21 A); dorsally with two narrow longitudinal grooves outlining a smooth, curved, broad dorsal surface with a weak narrow crest ( Fig. 21 A). Dorsal tentacles inserted at posterolateral margins of peristomium, more widely separated than in related species. First pair of branchiae lateral to tentacles on peristomium; second pair of branchiae on posterior margin of setiger 1, dorsal to notosetae; subsequent branchiae in similar positions ( Fig. 21 A).

Thorax with 4–6 narrow segments about 2x as wide as long; parapodia not elevated over dorsum as in many related species; dorsal surface not enclosed in a groove formed by parapodia; thoracic segments abruptly transitioning to abdominal segments that are as long as wide ( Figs. 21 A, 22A–D), then becoming longer than wide ( Fig. 21 B), some moniliform 1.5x as long as wide ( Figs. 21 B, 22A–D); far posterior segments narrowing to pygidium with a single lobe ( Figs. 21 B, 22A).

Parapodia reduced to simple conical lobes from which setae emerge. Thoracic and anterior abdominal parapodia with simple capillary setae only; middle and posterior abdominal neurosetae becoming shorter, broader, and with fine denticles along one edge at about setiger 30 ( Fig. 21 C), these best observed with 1000x magnification and with Phase Contrast optics; individual denticles short, pointed toward apex of seta. Some abdominal notosetae observed with long stiff fibrils or serrations along one edge ( Fig. 21 D), these very regular in appearance.

Methyl Green stain. A spectacular MG staining pattern characterizes this species. The prostomium and lateral and dorsal sides of the peristomium develop a deep reticulated turquoise pattern followed by similar staining on the ventral and lateral sides of the thoracic parapodia ( Fig. 22 D); the two longitudinal grooves on either side of the peristomium stain a deep green; the thoracic parapodia are in effect banded ( Fig. 22 D). The reticulated pattern is due to embedded glands that are also stained by MG on most abdominal segments although being sparse; the pattern is not as intense as on anterior segments.

Etymology. The name franciscana refers to the proximity to the City of San Francisco of the sampling site, the San Francisco Deep Ocean Disposal Site.

Remarks. Kirkegaardia franciscana n. sp. is a unique species in the very small size, expanded and rounded shape of the anterior end, narrow abdominal region with moniliform segments, and the distinctive MG staining pattern. The denticulated neurosetae are few, usually no more than two or three per abdominal neuropodium and with the fine denticles observed only with at least 1000x magnification. The serrated notosetae are also few and observed only with 1000x. The long pointed serrations of these setae were initially thought to be merely splayed fibrils sometimes observed on capillaries of other cirratulids. However, the regularity and consistent size of these serrations finally suggested they were a consistent type of tooth or denticle. It needs to be stated, however, that none of these specimens were sexually mature and it is entirely possible that they are juveniles. In a program during which more than 180 quantitative benthic samples were collected over a period of 13 years, K. franciscana n. sp. was rare, identified only three times, and either larger adults were never collected or were not recognized. The MG pattern was used to set them aside for further study resulting in this description as a new species. In checking other cirratulids from the study that are larger and might overlap with the morphology of smaller specimens of K. franciscana n. sp., two species of Aphelochaeta were described by Doner & Blake (2009); only one of which had a MG pattern and it was entirely different from that of K. franciscana . Other species of Aphelochaeta are also known from this area (Blake unpublished); none of these has a MG pattern as distinctive as that of K. franciscana . Kirkegaardia carinata n. sp. occurs throughout the study area and also has a distinctive, but different MG staining pattern and a very different morphology (see below).

Biology. Kirkegaardia franciscana was collected only rarely over 13 years of monitoring at the San Francisco Deep-water Disposal site. The sediments where the species was collected are composed of fine silt. Throughout the study area the benthic fauna is dominated by a large suite of polychaetes of the families Paraonidae , Spionidae , Cossuridae , and cirratulids of the genus Chaetozone , most of which were described by Blake (2006). Ecology of the site was reported by Blake et al. (2009).

Distribution. Known only from lower slope depths off northern California 2237–2983 m.

Figures 21 and 22 about here

Figures

FIGURE 21. Kirkegaardia franciscana n. sp., holotype (LACM-AHF Poly 8921): A, anterior end, dorsal view; B, posterior end, dorsal view; C, denticulate neuroseta; D, serrated notoseta.

FIGURE 22. Kirkegaardia franciscana n. sp., paratypes (LACM-AHF Poly 8922): A, entire worm, right lateral view; B, same specimen, anterior end; C, anterior end, right lateral view of another specimen; D, same with Methyl Green staining patterns. A – C, stained with Shirlastain A; D, with Methyl Green.